[MTD] Fix fwh_lock locking

This is on a custom board with a mapping driver access to an ST
M50LPW080 chip. This chip is probed successfully with
do_map_probe("jedec_probe",...). If I use the mtdchar interface to
perform unlock->erase->program->lock on any of the 16 eraseblocks in the
chip, the chip is left in FL_STATUS mode while the data structures
believe that the chip is in FL_READY mode. Hence, any subsequent reads
to any flash byte results in 0x80 being read.

Signed-off-by: Shashi Rao <shashi@sun.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>